There are some great posts in this thread.
I'd like to second what MudPaint mentioned about ring etiquette. A standard for most busy facilities is 1.) the lesson student has the right of way. 2.) the least experienced or proficient rider has the right of way.
So if you and your instructor have carved out an area of the ring for your lesson, and you're cantering on an obvious track, the other riders should be looking out for you and getting out of your way.
In re: the various instructors, I think you need to ask yourself some tough questions. When you ride with the intense instructor, do you finish up feeling good about yourself and your lessons? Is she challenging you, or intimidating you? The former's good, the latter, not so much. And are you getting somethign from her that you're not getting from the other instructors, or is she just adding to your performance anxiety? Also consider that there are different instructors that are best at different times/different levels of riding. She might be the perfect instructor for you in six months, but not so perfect right now.
Last edited by maura; 11-14-2011 at 07:39 AM.